Many different types of data storage media have been developed to store information. Traditional media, for instance, include magnetic media, optical media, and mechanical media to name a few. Increasing data storage density is a paramount goal in the development of new or improved types of data storage media.
In traditional media, individual bits of information are stored as distinct mechanical, optical, or magnetic changes on the surface of the media. For this reason, data storage medium surface area imposes physical limits on data densities for a given recording technique.
Holographic data storage media can offer higher storage densities than traditional media. In a holographic medium, data can be stored throughout the volume of the medium rather than the medium surface. In other words, holographic media permit three-dimensional data storage. Theoretical holographic storage densities can approach tens of terabits per cubic centimeter.
In holographic data storage media, entire pages of information, e.g., bitmaps, can be stored as optical interference patterns within a photosensitive recording material. This can be done by intersecting two coherent laser beams within the recording material. The first laser beam, called the object beam, contains the information to be stored; and the second, called the reference beam, interferes with the object beam to create an interference pattern that can be stored in the recording material as a hologram. When the stored hologram is later illuminated with only the reference beam, some of the light of the reference beam is diffracted by the holographic interference pattern. Moreover, the diffracted light creates a reconstruction of the original object beam. Thus, by illuminating a recorded hologram with the reference beam, the data encoded in the object beam can be recreated and detected by a data detector such as a camera.
Holographic data storage media typically have a sandwiched construction in which a photosensitive recording material is sandwiched between two substrates. The holograms are recorded and stored in the photosensitive material. By improving the formulation of the photosensitive material, holographic media can be improved. In particular, improved formulations are desirable to increase storage densities of holographic media, and/or to improve environmental stability.